1. Field of the Invention
This invention relates to a process for changing the stereoisomeric content of cycloaliphatic diamines and is more particularly concerned with increasing the proportion of trans,trans-stereoisomer in a mixture of stereoisomers of di-(p-aminocyclohexyl)methane.
2. Description of the Prior Art
Di-(p-aminocyclohexyl)methane is generally prepared by the catalytic hydrogenation of di-(p-aminophenyl)methane; see, for example, U.S. Pat. Nos. 2,494,563; 2,606,924; 2,606,928; 3,591,635 and 3,856,862. The products so obtained are found to be mixtures of the various possible stereoisomers, namely, the cis,cis-, cis,trans- and trans,trans-isomers.
For many purposes it is desirable to employ the substantially pure trans,trans-isomer. For example, polyamides derived from the latter isomer and dibasic aliphatic and aromatic carboxylic acids produce synthetic fibers having highly desirable properties; see, for example, Tedder et al., Basic Organic Chemistry, Part 5, pp. 283-4, John Wiley and Sons, London, 1975. Various methods are known for separating the more desirable trans,trans-isomer from the other isomers; see, for example, French specification No. 2,012,261 (Chem. Abstracts, 73, 130691, 1970) and German OLS 1,810,924 (Chem. Abstracts, 73, 66133, 1970). It is obviously desirable to seek to increase the trans,trans-isomer content in a mixture of this and the other stereoisomers before subjecting said mixture to separation for the isolation of the trans,trans-isomer. The process of this invention is directed to this object, namely, to a method of enriching the trans,trans-isomer in a mixture of the stereoisomers of di-(p-aminocyclohexyl)methane.